This invention relates to antenna systems, and more particularly to techniques for dynamic signal routing in Electronically Scanned Antenna (ESA) systems.
In a multifunction tactical radar, dynamic signal routing between a multiport antenna and a bank of receivers is usually accomplished by an RF switch network. Unavoidable switch non-idealities such as impedance mismatches, signal attenuation, signal leakage, and dynamic range limitations are drawbacks to this approach and usually have significant radar system performance implications. The switches themselves also introduce undesirable single point failure modes.
FIG. 1 shows a conventional system architecture having an electronically scanned antenna partitioned into four quadrants (Quad 1, Quad 2, Quad 3, Quad 4) feeding a conventional monopulse combiner. The outputs of the monopulse combiner are Sum (Quad 1+Quad 2+Quad 3+Quad 4), Delta Azimuth (Quad 1+Quad 3xe2x88x92Quad 2xe2x88x92Quad 4), Delta Elevation (Quad 1+Quad 2xe2x88x92Quad 3xe2x88x92Quad 4), and Delta X (Quad 1+Quad 4xe2x88x92Quad 2xe2x88x92Quad 3). These signals are typically connected to a bank of receivers via a switch network, as shown. The switch network provides the desired dynamic routing of the antenna outputs to the individual receivers. In some cases, the sum channel would be directly connected to a receiver to avoid the switch losses, reflections, distortions, and leakage in the sum signal path resulting in a loss of system availability if that receiver fails.
The conventional approach has several drawbacks overcome by this invention. The non-idealities of the RF circuits and switches used in the switch network degrade the radar return signals at a critical point in the signal path, significantly affecting radar performance. The switch network includes single point failure mechanisms that could render one or more of the critical antenna monopulse signals inoperative, likely degrading system performance below useful levels. The addition of the switch network increases system cost and complexity.
An array system with dynamic signal routing is described, and includes a plurality of antenna elements divided into a plurality of subarrays. A summing network for each subarray combines the signals from each antenna element in a subarray to provide for each subarray a subarray signal. Phase shifting apparatus selectively introduces a signal routing phase shift of 0xc2x0 or 180xc2x0 to the respective subarray signals. A monopulse combiner is responsive to the subarray signals to provide a plurality of combiner outputs. The system can include a plurality of receivers each having an input connected to receive a corresponding combiner output for processing the monopulse combiner outputs. A controller providing phase shift commands to the phase shifting apparatus to modulate the phase shift of the phase shifters of selected subarrays by adding a subarray phase shift of 0xc2x0 or 180xc2x0 to dynamically effect the routing of the monopulse array output signals to desired ones of the receivers.
Modern multifunction tactical radars employ ESAs that are partitioned into subarrays. The ability to dynamically rout the various antenna array and subarray outputs to a bank of receivers is very desirable. Dynamic signal routing in accordance with the invention allows the antenna outputs to be time multiplexed between fewer receivers than the total number of antenna outputs. This flexible signal routing also allows reconfiguration to compensate for failed receivers.
In accordance with an aspect of the invention, an ESA is described with dynamic signal routing to a set of receivers. A monopulse ESA has a plurality of antenna elements divided into subarrays. ESA beam steering phase shifters are associated with the respective subarrays of antenna elements, such that the output signals from the respective antenna elements associated with the respective subarrays are phase shifted and summed to provide respective subarray signals. A monopulse combiner responsive to the subarray signals provides monopulse outputs to the set of receivers. A beam steering controller provides phase shift commands to the ESA phase shifters to set the phase shift associated with the respective phase shifters of the subarrays. In addition to supplying a beam steering phase shift to each ESA phase shifter, the controller commands the ESA phase shifters to modulate the phase shift of selected subarrays. The phase shifts associated with the subarrays are selectively set to either 0 or 180 degrees relative to the one of the subarrays by adding the desired subarray phase shift (0 or 180 degrees) to the beam steering phase shift at each element.
In an exemplary embodiment, the subarrays represent quadrants, and the monopulse output signals are Sum, Delta Azimuth, Delta Elevation, and Delta X; by setting the quadrant phase shifts, the monopulse output signals are appropriately steered to the desired receivers.
The dynamic signal routing technique can also be applied to arrays which are not electronically scanned.